Battery control device

ABSTRACT

A battery control device capable of obtaining an allowable charge/discharge current value can further accurately reflect a polarization state of a battery. A battery controller includes a first allowable current value calculation unit, a battery equivalent circuit model, and a correction amount calculation unit. Assuming a non-polarization state, a current limit value of the battery based on an open circuit voltage and upper and lower limit voltages set in the battery, the first allowable current value calculation unit calculates a first allowable current value Imax1. The battery equivalent circuit model estimates a polarization state of the battery when the current limit value is being calculated. The correction unit calculates an allowable current value correction value based on the estimated polarization state for correcting Imax1. A second allowable current value Imax2 which is the corrected first allowable current value is output as an allowable charge/discharge current value of the battery.

TECHNICAL FIELD

The present invention relates to a battery control device of a batterysystem.

BACKGROUND ART

In recent years, battery systems incorporating a large number ofbatteries, such as power storage devices for moving objects, powerstorage devices for stabilizing grid interconnection, and emergencypower storage devices, have attracted attention. To derive performanceof these systems, parameters such as a battery charge rate (hereinafterreferred to as SOC), a deterioration rate (SOH), a maximumchargeable/dischargeable current (allowable current value) arecalculated and used for battery control, or it is necessary to properlyequalize the charge rate of each battery.

To realize the above, a circuit (cell controller) for battery voltagemeasurement is attached to each battery, and based on information sentfrom these cell controllers, a battery controller mounting a centralprocessing unit (CPU) performs the above-described calculation andoperation. The calculation of the allowable current value is part of asafety function to prevent overvoltage of a battery, and safety of abattery system is maintained by limiting a current so as not to exceedthe allowable current value.

To calculate the maximum current at which the battery does not becomeovervoltage, the internal state and parameters of the battery such as anopen current voltage (hereinafter referred to as OCV) of the battery andinternal resistance information. In particular, it is necessary toinfluence a polarization voltage generated in the battery in a powerstorage device for a moving object in which irregular current alwaysflows. Considering calculation performance of the above-described CPU,it is particularly required to calculate a safe current in considerationof influence of an OCV, an internal resistance, and a polarizationvoltage in calculation of allowable current value for a moving objectwith a small calculation amount. However, to calculate the polarizationvoltage, it is necessary to use a function having a large calculationamount such as an exponential function and therefore difficult tocalculate with the CPU.

Therefore, a method has been proposed in which a time during which acurrent continuously flows in a battery is measured, and a resistancevalue to be used for calculation of an allowable current value isreferred to from a resistance value table reflecting influence of apolarization voltage by using the measured time (for example, refer toPTL 1). According to this, the allowable current value can be calculatedwith a small calculation amount without using an exponential function orthe like. Further, as disclosed in PTL 1, a method is used in which afixed resistance value corresponding to a sufficiently largepolarization voltage is used for applications in which a currentcontinuously flows for a short time as in a hybrid vehicle. Throughthese methods, it is possible to calculate, with a small calculationamount, a current which does not cause a battery to become overvoltageeven when a polarization voltage exists.

CITATION LIST Patent Literature

PTL 1: WO 2012/169063 A

SUMMARY OF INVENTION Technical Problem

Meanwhile, in the invention described in PTL 1, to reflect the influenceof a polarization voltage on an allowable current value calculation, aresistance value in the case where a current continuously flows for acertain period of time is used. However, in reality, a charging period,a discharging period, and a pausing period may be switched in a timeshorter than the assumed certain time, and the actual resistance valuetends to be smaller than the assumed resistance value. Therefore, anallowable current value may be excessively limited in some cases.

Solution to Problem

A battery control device according to the present invention includes acurrent limit value calculation unit, an estimation unit, and acorrection unit. The current limit value calculation unit calculates acurrent limit value of a battery assuming a non-polarization state,based on an open circuit voltage of the battery and upper and lowerlimit voltages set in the battery. The estimation unit estimates apolarization state of the battery at the time of calculating the currentlimit value. The correction unit corrects the current limit value basedon the estimated polarization state. The battery control device outputsthe current limit value corrected by the correction unit as an allowablecharge/discharge current value of the battery.

Advantageous Effects of Invention

According to the present invention, it is possible to obtain anallowable charge/discharge current value further accurately reflecting apolarization state of a battery.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an embodiment of a battery system.

FIG. 2 is a block diagram describing a configuration for calculating anallowable current value.

FIG. 3 is a diagram illustrating an example of a battery equivalentcircuit model.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described below withreference to drawings. FIG. 1 is a diagram illustrating an embodiment ofa battery system 100 and indicates an example of a battery system usedfor a battery power supply device. An output voltage of the batterysystem 100 is a direct current voltage which varies depending on aremaining capacity and an output current of a battery and therefore maynot be suitable for directly supplying electric power to a load 111.Therefore, in the example indicated in FIG. 1, an inverter 110 convertsthe output voltage of the battery system 100 into three-phasealternating current and supplies the current to the load 111. A hostcontroller 112 that controls the inverter 110 and the entire powerconverter controls.

The same configuration is applied in the case where a direct currentvoltage, another polyphase alternating current, or a single-phasealternating current is supplied to the load. In addition, when the load111 outputs electric power, it is possible to store the electric poweroutput by the load 111 in the battery module 105 by using the inverter110 as a bidirectional inverter. Further, the battery module 105 can becharged as necessary by connecting a charging system to the batterysystem 100 in parallel with the inverter 110.

The battery system 100 transmits, to the host controller 112, a chargingrate (SOC) and a deterioration rate (SOH) of a battery useful forcontrolling the inverter 110 and the load 111, a maximumcharge/discharge current (allowable current value) which can flow intothe battery, a battery temperature, information on a battery state suchas the presence or absence of abnormality of the battery. The hostcontroller 112 performs such as energy management and abnormalitydetection on the basis of these pieces of information. Further, the hostcontroller 112 transmits a disconnection instruction to the batterysystem 100 when the host controller 112 determines that the batterysystem 100 should be disconnected from the inverter 110 or the load 111.

The battery system 100 includes a battery module 105, a batterycontroller 101, a relay 106, a current sensor 108, a voltage sensor 102,a leakage sensor 103, a circuit breaker 107, and a temperature sensor161. At least one battery module 105 which includes a plurality ofbatteries is included. The battery controller 101 monitors, estimates,and controls a state of the battery system 100. The relay 106 intermitsoutput of the battery system 100. The current sensor 108 measures acurrent flowing into a battery. The voltage sensor 102 measures abattery voltage. The leakage sensor 103 measures an insulationresistance between the battery system 100 and, for example, the ground.The circuit breaker 107 is provided in response to an output voltage ofthe battery system 100. The temperature sensor 161 measures a batterytemperature. The battery controller 101 includes a CPU 601 and a storageunit 602. The CPU 601 performs various calculations. The storage unit602 stores battery parameters to be described later. The battery system100 illustrated in FIG. 1 includes two battery modules 105 connected inseries via the circuit breaker 107.

The battery module 105 has a plurality of unit cells and has a circuitfor measuring a temperature inside the module and a voltage of each unitcell, and a circuit for performing charge and discharge for each unitcell as needed. This makes it possible to perform voltage monitoring andvoltage adjustment for each unit cell and to measure temperatureinformation necessary for estimating a battery state in whichcharacteristics change according to a temperature. Details will bedescribed later.

The current sensor 108 and a pair of the relays 106 are connected inseries to the battery modules 105 connected in series. The currentsensor 108 measures a current value necessary for monitoring/estimatinga state of the battery module 105. By controlling opening and closing ofa pair of the relays 106 based on an instruction of the host controller,it is possible to shut off or connect output of the battery system 100.In the case where a voltage of the battery module 105 is high, forexample, 100 V or more, the circuit breaker 107 may be added to manuallyshut off power input/output to the battery system 100. By forciblyshutting off the input/output by using the circuit breaker 107, it ispossible to prevent occurrence of an electric shock accident or ashort-circuit accident at the time of assembling or disassembling thebattery system 100 or when handling an accident of a device mounting thebattery system 100.

In the case where a plurality of the battery modules 105 are connectedin parallel, the relay 106, the circuit breaker 107, and the currentsensor 108 may be provided in each row, or the relay 106, the circuitbreaker 107, and the current sensor 108 may be provided only in anoutput portion of the battery system 100. In addition, the relay 106,the circuit breaker 107, and the current sensor 108 may be provided bothin each row and the output portion of the battery system 100.

The relay 106 may be formed of one relay or formed of a combination of amain relay, a precharge relay, and a resistor. In the latterconfiguration, the resistor is placed in series with the prechargerelay, and these are connected in parallel with the main relay. Then,when the relay 106 is connected, first the precharge relay is connected.Since the current flowing through the precharge relay is limited by theresistor connected in series. Therefore, an inrush current which canoccur in the former configuration can be limited. Then, after thecurrent flowing through the precharge relay becomes sufficiently small,the main relay is connected. The timing of connecting the main relay maybe based on the current flowing through the precharge relay or may bebased on a voltage applied to the resistor or a voltage betweenterminals of the main relay. Further, the timing may be based on thetime elapsed since the precharge relay is connected.

The voltage sensor 102 measures a voltage value necessary for monitoringand estimating a state of the battery module 105. The voltage sensor 102is connected in parallel to one or a plurality of battery modules 105 orconnected in parallel to each series of the battery modules 105. Inaddition, the leakage sensor 103 is connected to the battery module 105,and a state in which electric leakage can occur, that is, a state inwhich an insulation resistance is lowered, can be detected beforeelectric leakage occurs. As a result, occurrence of an accident can beprevented.

Measurement values by the battery module 105, the current sensor 108,the voltage sensor 102, and the leakage sensor 103 are transmitted tothe battery controller 101. The battery controller 101 monitors andestimates a battery state and controls the battery system 100, based onthe received measurement values. Here, the control means, for example,charging and discharging for each unit cell for equalizing a voltage ofeach unit cell, power source control of each sensor, addressing of thesensor, and control of the relay 106 connected to the battery controller101. The CPU 601 performs calculations necessary for monitoring,estimating and controlling the battery state.

The battery system 100 may include a system cooling fan, and the batterycontroller 101 may control the fan. Since the battery system 100performs cooling in this manner, the amount of communication with thehost controller can be reduced.

In the example illustrated in FIG. 1, although the voltage sensor 102and the leakage sensor 103 are made to be separate parts from thebattery controller 101 to have a degree of freedom in configuration, thebattery controller 101 may have a configuration in which the voltagesensor 102 and the leakage sensor 103 are incorporated in the batterycontroller 101. By adopting the incorporation configuration, the numberof harnesses is reduced as compared with the case of preparingindividual sensors, and the labor of attaching the sensor can also bereduced. However, by incorporating the sensor, the scale (maximum outputvoltage, current, etc.) of the battery system 100 in which the batterycontroller 101 can control may be limited. In such a case, the sensorsare preferably separate parts.

FIG. 2 is a block diagram describing a configuration for calculating anallowable current value. The allowable current value calculation isperformed by the CPU 601. As a functional configuration, the CPU 601includes a battery equivalent circuit model 702, a first allowablecurrent value calculation unit 704, a polarization prediction unit 705,a correction amount calculation unit 706, and a second allowable currentvalue calculation unit 707. A database 703 is a battery parameter storedin the storage unit 602.

The battery equivalent circuit model 702 is an equivalent circuit modelfor expressing the internal state of a unit cell. The first allowablecurrent value calculation unit 704 calculates a first allowable currentvalue when there is no polarization in a battery. The polarizationprediction unit 705 predicts polarization of a battery after a certainperiod of time. The correction amount calculation unit 706 calculatesthe influence of a polarization on the first allowable current valuecalculated by the first allowable current value calculation unit 704 asa correction value (allowable current value correction value). Thesecond allowable current value calculation unit 707 corrects theallowable current value calculated by the first allowable current valuecalculation unit 704 with the allowable current value correction valuecalculated by the correction amount calculation unit 706 and outputs thecorrected value as the second allowable current value.

The battery equivalent circuit model 702 estimates and outputs an SOC,an OCV, and a polarization voltage of a unit cell based on a currentvalue measured by the current sensor 108, a battery temperature measuredby the temperature sensor 161, and a battery closed circuit voltage(hereinafter referred to as a CCV) measured by the voltage sensor 102.As the CCV, a CCV converted from a voltage value measured by the voltagesensor 102 per unit cell or a CCV for each unit cell can be used. Byusing such the battery equivalent circuit model 702, the internal stateof a unit cell which cannot be observed directly can be estimated, andthe estimated value can be used for other processing.

FIG. 3 is a diagram illustrating an example of the battery equivalentcircuit model 702. In the example illustrated in FIG. 3, an OCV isdenoted by a voltage source 751, a DC resistance is denoted by aresistor 752, a polarization resistance is denoted by a resistor 753,and a polarization capacity is denoted by a capacitor 754. These valueschange with deterioration of a battery, and therefore values accordingto deterioration are used. By applying an initial voltage to the batteryequivalent circuit model 702 as the OCV, a polarization is initializedto a zero state. By continuously applying a current value measured bythe current sensor 108 to the battery equivalent circuit model 702, thebattery equivalent circuit model 702 can express the current batterystate. Consequently, a polarization voltage can be calculated.

For example, a correlation table between an SOC and an OCV is stored inadvance, and an initial value of the SOC is obtained from thiscorrelation table and the OCV fetched as the initial voltage. Duringoperation, for example, the SOC is estimated from the initial valuethereof and the integrated current value. From the estimated SOC and thecorrelation table, it is possible to estimate the OCV in operation.

In the example illustrated in FIG. 3, a term of the polarization isassumed to be one. However, by using a plurality of terms, thecalculation can be made more accurate. In initialization, the initialvalue of an electric charge accumulated in the capacitor 754 is set tozero. This is because there is a pause time generally sufficientlylonger than a time constant of a battery before a system is started, andthe capacitor 754 is completely discharged. The initialization isperformed at the timing when the relay 106 is open, such as when thebattery system 100 is activated or when an initialization command valueis received from the host controller 112.

Returning to FIG. 2, the database 703 outputs upper and lower limitvoltages needed for calculation of an allowable current value, and afirst resistance and a first gain to be described later, based on theSOC output from the battery equivalent circuit model 702, thetemperature output from the temperature sensor 161, and the currentoutput from the current sensor 108. The OCV, the SOC, and thepolarization voltage output from the battery equivalent circuit model702 correspond to the present battery state. Therefore, the upper andlower limit voltages, the first resistance, and the first Gain outputfrom the database 703 also correspond to the present battery state. Byusing these output values, the allowable current value can be calculatedaccording to the battery state.

In this manner, by obtaining output data values based on a map, it ispossible to reduce the amount of calculation and to deal withcharacteristics whose theoretical expression is unknown. Further, thevalues may be output by an approximation expression. As a result, theamount of data can be reduced, and the accuracy of output values can beimproved.

The first allowable current value calculation unit 704 calculates thefirst allowable current value Imax1 based on the OCV output by thebattery equivalent circuit model 702, the upper and lower limit voltagesoutput by the database 703, and the first resistance. The formula (1)indicates an example of a calculation formula of the allowable chargecurrent Icmax1.

Icmax1=(Vmax−OCV)/R1  (1)

In the formula (1), Vmax indicates an upper limit voltage, and R1indicates a first resistance. Here, the first resistance R1 is aresistance value (internal resistance) of a battery estimated after aconstant current has flowed for a predetermined time, assuming that theconstant current flows from an initialized non-polarization state. Inthe present embodiment, a value of the first resistance R1 is obtainedin advance by such as an experiment and a simulation, and the value isstored in the database 703.

The internal resistance of a battery at the time of calculation(present) is an internal resistance in the state in which a polarizationis zero, and therefore it is smaller than the first resistance R1. Thatis, the allowable charge current Icmax1 calculated by the formula (I) issmaller than the allowable charge current (allowable charge currentcalculated by substituting the present internal resistance into theformula (1)) according to the present battery state. Then, in the casewhere a constant current continues to flow from the non-polarizationstate, when a predetermined time has elapsed, the calculated allowablecharge current reaches Icmax1.

The allowable discharge current Idmax1 is considered in the same manneras in the case of the allowable charge current Icmax1 and is calculatedby the following formula (2). Vmin indicates a lower limit voltage. Inthe formula (2), the internal resistance after a lapse of apredetermined time is set to be the same first resistance R1 as in thecase of charging. However, in an actual battery, the values aredifferent between a charging direction and a discharging direction, andit is preferable to use a value corresponding to a current direction.

Idmax=(OCV−Vmin)/R1  (2)

In this manner, by controlling the charge/discharge current by theallowable current value (allowable charge current value, and allowabledischarge current value) Imax1 calculated by using the first resistanceR1, as long as the maximum current is continuously used within thisrange, a CCV does not reach the upper and lower limit voltages until thelapse of a predetermined time.

The first allowable current value Imax1 calculated by the firstallowable current value calculation unit 704 is an allowable currentvalue in the case where it is assumed that the current battery is in anon-polarization state. Therefore, when the present time is a time pointafter the lapse of a period of time from the initialization timing, thebattery is not in a non-polarization state at the present time, andtherefore an error occurs. Therefore, the following correctionprocessing is performed by providing the polarization prediction unit705, the correction amount calculation unit 706, and the secondallowable current value calculation unit 07 such that an accurateallowable current value can be obtained even when a battery is not in anon-polarization state at the present time.

Further, in the above-described first allowable current valuecalculation unit 704, the first allowable current value Imax1 iscalculated by using the first resistance R1 when a constant currentflows for a predetermined time. In general, the following formula (3)using an exponential function needs to be used to predict a polarizationvoltage after a predetermined time when a constant current flows. Here,Vpt indicates a polarization voltage after a predetermined time, Rpindicates a polarization resistance, I indicates a current, Vp0indicates a polarization voltage as at the present time, Cp indicates apolarization capacity, and t indicates a predetermined time.

Vpt=IRp−(IRp−Vp0)exp(−t/RpCp)  (3)

When the right side of the formula (3) is divided into a term notincluding the polarization voltage Vp0 and a term including thepolarization voltage Vp0, the following formula (4) is obtained. In thiscase, Gt=exp (−t/RpCp). In the formula (4), when I=0, Vpt=Vp0·Gt. When acurrent flowing in a battery is zero, a polarization voltage decreaseswith the lapse of time. Then, the polarization voltage of the value Vp0decreases with the lapse of time and becomes Vpt=Vp0·Gt when thepredetermined time t passes. As described above, the first gain Gt is aparameter expressing a temporal change (attenuation) in a polarizationvoltage and is a constant determined by the magnitude of thepredetermined time t.

Vpt=IRp(1−Gt)+Vp0·Gt  (4)

The relationship among the OCV, the CCV, and the Rdc in FIG. 3 isexpressed by using the formula (4), as indicated in the followingformula (5). I indicates a current flowing through a battery.

CCV=OCV+I·Rdc+Vpt=OCV+I·Rdc+IRp(1−Gt)+Vp0·Gt=OCV+I(Rdc+Rp(1−Gt))+Vp0·Gt  (5)

The first allowable current value Icmax1 calculated by the firstallowable current value calculation unit 704 is considered to be Vp0=0in the formula (5) and corresponds to the case where the portion of“Rdc+Rp (1−Gt)” of the second term is regarded as the first resistanceR1. Then, the third term of the formula (5)=Vp0·Gt is a voltagedependent on the polarization voltage Vp0 at the present point in timeand is calculated by the polarization prediction unit 705. In thepresent embodiment, Gt is referred to as a first gain, and the thirdterm=Vp0·Gt is referred to as a first polarization voltage. Thepolarization voltage Vp0 is calculated by the battery equivalent circuitmodel 702, and the first gain Gt is output from the database 703.

That is, the polarization prediction unit 705 calculates a firstpolarization voltage (Vp0·Gt) which is a polarization voltage after thelapse of the predetermined time t, based on the polarization voltage Vp0at the present time output from the battery equivalent circuit model 702and the first gain Gt output from the database 703. When a battery withthe polarization voltage Vp0 is left in a zero current state, thepolarization voltage gradually decreases. However, the polarizationvoltage after the lapse of the predetermined time t is the firstpolarization voltage (Vp0·Gt).

In this manner, by outputting the first gain Gt expressed by anexponential function from the database 703, an exponential function witha large calculation amount can be made unnecessary, and even in anembedded CPU which is restricted in a calculation capability, apolarization voltage after the lapse of a certain period of time can beeasily calculated.

The correction amount calculation unit 706 calculates the influence of apolarization on the first allowable current value Imax1 calculated bythe first allowable current value calculation unit 704 as an allowablecurrent value correction value ΔI. As described above, the firstallowable current value Imax1 is a current value in the case where Vp0=0in the formula (5). Therefore, allowable current value in the case ofVp0□0 (that is, the allowable current value obtained after correction)is smaller than the first allowable current value Imax1 by the allowablecurrent value correction value ΔI. Here, the allowable current valueobtained after correction is referred to as a second allowable currentvalue Imax2.

By substituting CCV=Vmax and I=Icmax2 in the formula (5), the followingformula (6) is obtained. That is, the allowable current value correctionvalue ΔI is calculated as ΔI=Vp0·Gt/R1.

Icmax2=(Vmax−OCV)/(Rdc+Rp(1−Gt))−Vp0·Gt/(Rdc+Rp(1−Gt))=(Vmax−OCV)/R1−Vp0·Gt/R1  (6)

The second allowable current value calculation unit 707 subtracts theallowable current value correction value ΔI calculated by the correctionamount calculation unit 706 from the first allowable current value Imax1calculated by the first allowable current value calculation unit 704 andoutputs the second allowable current value Imax2 expressed by theformula (6).

In this manner, in the present embodiment, the first allowable currentvalue calculated on the assumption that a polarization as at the presenttime is in a non-polarization state is corrected with the allowablecurrent value correction value ΔI calculated based on the polarizationvoltage Vp0 at the present point in time, and a current during chargeand discharge is controlled by using the corrected second allowablecurrent value Imax2. Since the second allowable current value Imax2 iscalculated according to the polarization state of a battery, it ispossible to further precisely calculate the largest current (that is,the allowable current value) at which a CCV does not reach the upper andlower limit voltages even if a current continues to flow for apredetermined time. In the above description, the predetermined time tis described in the case of t□0 as an example. However, it can also beapplied in the case of t=0.

Conventionally, when an allowable charge/discharge current in thebattery state as at the present time is calculated, it is necessary toaccurately know an internal resistance as at the present time. Forexample, when the allowable charge current is calculated in the batterystate as at the present time, it can be calculated by using the internalresistance as at the present time instead of the first resistance in theformula (1). Although the internal resistance depends on thepolarization state of a battery, in the technique described in theabove-described PTL 1, instead of estimating polarization state as atthe present time, the internal resistance of the battery after aconstant current has flowed for a certain time is used.

For example, in a battery system mounted in a hybrid vehicle, a currentis charged and discharged at intervals of about several seconds to tenseconds. Therefore, for example, the internal resistance when a current(for example, 200 A) capable of being output by a battery flows forabout 3 to 5 seconds is used. Therefore, a smaller allowable chargecurrent is calculated than the allowable charge current on the basis ofa battery state at the time of calculation. That is, the charge currentis limited more than necessary.

In conventional techniques, the value of allowable current which canflow in “this moment” is calculated. However, from the viewpoint ofenergy management or the like, it is recently requested to calculate avalue of allowable current which can continuously flow for “a certainperiod of time from now”. As in a conventional manner, the value ofallowable current which can flow in “this moment” is calculated.Therefore, when control is performed based on the allowable currentvalue, a constant current may not continuously flow within an allowablecurrent value range “from now to a predetermined time”. On the otherhand, in the present embodiment, an allowable current which cancontinuously flow for a predetermined time from the present time can becalculated. Therefore, it is possible to certainly perform control untilthe predetermined time with a current within the allowable current valuerange.

The predetermined time in the present embodiment is set according to theuse environment of the battery system 100. For example, in the casewhere the system is used in a hybrid vehicle, the predetermined time isapproximately set to the time during which charge and dischargepredicted in a general vehicle use situation can be continued. Theconstant current value is also set in consideration of the current valuerequired according to the general vehicle use situation. The set valuesregarding the predetermined time and the constant current are input fromthe host controller 112 illustrated in FIG. 1.

Further, the correction amount calculation unit 706 calculates influenceof a polarization voltage on an allowable current value. In the exampleindicated in FIG. 2, the correction amount calculation unit 706calculates the allowable current value correction value GI by using, aspolarization information, the first polarization voltage Vp0·Gt when thepredetermined time t has elapsed. Therefore it is possible to calculatea value of allowable current (the second allowable current value Imax2)which can certainly continue to flow for the certain time.

Although it is different from the processing indicated in FIG. 2, aspolarization information, instead of the first polarization voltageVp0·Gt, the polarization voltage Vp0 output from the battery equivalentcircuit model 702 is input to the correction amount calculation unit706, and the allowable current value correction value ΔI may becalculated as ΔI=Vp0/R1. This corresponds to using the first gain whenGt(0)=1, that is, t=0. Since the first gain Gt is Gt=exp(−t/RpCp), thegain is the largest when t=0 and decreases with the lapse of time.Therefore, when the polarization voltage Vp0 is used as the polarizationinformation, the polarization voltage is estimated to be large.Therefore, although the allowable current value decreases, safety can befurther certainly assured.

By using the polarization voltage multiplied by a fixed value, influenceof the polarization voltage can be adjusted, and overvoltage due to apolarization voltage estimation error of the battery equivalent circuitmodel 702 can be prevented.

In the above-described embodiment, a value of the first resistance R1corresponding to the internal resistance of a battery is stored in thedatabase 703. However, from the DC resistance Rdc of the battery, an OCVchange rate Gsoc per unit current (hereinafter called a second gain),the polarization resistance Rp, and the first gain Gt, the firstresistance R1 may be obtained by calculation as the formula (7). Byindirect calculating the first resistance R1 in this manner, it ispossible to handle parameter changes due to such as deterioration of abattery. Although the description of the second gain Gsoc, which is theOCV change rate per unit current, is omitted in the above-describedformula (5), to express the first resistance R1 further accurately, thesecond gain Gsoc is preferably considered as the formula (7).

R1=Rdc+Gsoc+Rp(1−Gt)  (7)

In the above-described embodiment, the following operational effects canbe obtained. (a) The battery controller 101 which is a battery controldevice includes the first allowable current value calculation unit 704,the battery equivalent circuit model 702, the polarization predictionunit 705, the correction amount calculation unit 706, and the secondallowable current value calculation unit 707. The first allowablecurrent value calculation unit 704 calculates a first allowable currentvalue which is a current limit value of a battery assuming anon-polarization state based on an open circuit voltage (OCV) of thebattery and upper and lower limit voltages (Vmax and Vmin) set in thebattery. The battery equivalent circuit model 702 estimates apolarization state of the battery at the time of calculating the currentlimit value. The polarization prediction unit 705 operates as acorrection unit to correct the first allowable current value based onthe estimated polarization state. Then, the corrected first allowablecurrent value, that is, the second allowable current value Imax2, isoutput as an allowable charge/discharge current value of a battery.

The first allowable current value calculated on the assumption that apolarization as at the present time is in a non-polarization state iscorrected by the allowable current value correction value ΔI calculatedbased on the polarization voltage Vp0 as at the present time. Therefore,an accurate allowable current value according to a battery state can becalculated.

(b) Further, the first allowable current value calculation unit 704calculates the first allowable current value of a battery based on theopen circuit voltage (OCV) of the battery, the upper and lower limitvoltages (Vmax, Vmin) set in the battery, and the first resistance R1which is a battery internal resistance in the case where a constantcurrent flows in the battery from a non-polarization state for apredetermined time. The polarization prediction unit 705 calculates thefirst polarization voltage Vp0·Gt at the time when a battery in apolarization state estimated by the battery equivalent circuit model 702is maintained in a current zero state for the predetermined time, andthe first allowable current value may be corrected by using theallowable current value correction value ΔI corresponding to thecalculated first Polarization voltage Vp0·Gt

As a result, it is possible to calculate an allowable current value(allowable charge/discharge current value) whereby constant currentcontinuously flows for a predetermined period of time from the presenttime and perform control at a current within the allowable current valuerange until the predetermined time. Incidentally, the allowable currentvalue correction value ΔI may be calculated as ΔI=Vp0·Gt/R1 by using thefirst resistance R1 which is a battery internal resistance and the firstpolarization voltage Vp0·Gt.

(c) Further, the first resistance R1 which is a battery internalresistance may be calculated by the above-described formula (7), basedon the DC resistance Rdc of a battery, the second gain Gsoc which is anopen circuit voltage change amount per unit current of the battery, andthe polarization resistance Rp of the battery. Calculating the firstresistance R1 in this manner makes it possible to deal with parameterchanges due to deterioration of a battery or the like.

(d) In addition, at least one of the first resistance R1 which is abattery internal resistance, the first gain Gt which is a coefficientindicating a temporal change in a polarization voltage when a batterycurrent is zero, and upper and lower limit voltages may be set to avalue according to at least one of a temperature of a battery, acharging rate (SOC) of the battery, and a current flowing in thebattery.

Although various embodiments and modifications have been describedabove, the present invention is not limited to these contents. Otherembodiments considered within technical ideas of the present inventionare also included within the scope of the present invention.

REFERENCE SIGNS LIST

-   100 battery system-   101 battery controller-   102 voltage sensor-   105 battery module-   108 current sensor-   161 temperature sensor-   601 CPU-   602 storage unit-   702 battery equivalent circuit model-   703 database-   704 first allowable current value calculation unit-   705 polarization prediction unit-   706 correction amount calculation unit-   707 second allowable current value calculation unit-   Imax1 first allowable current value-   Imax2 second allowable current value-   Gsoc OCV change rate (second gain)-   Gt first gain-   R1 first resistance-   Vmax upper limit voltage-   Vmin lower limit voltage-   Vp0 polarization voltage-   Vp0·Gt first polarization voltage-   ΔI allowable current value correction value

1. A battery control device, comprising: a current limit valuecalculation unit configured to calculate a current limit value of abattery assuming a non-polarization state, based on an open circuitvoltage of the battery and upper and lower limit voltages set in thebattery; an estimation unit configured to estimate a polarization stateof the battery at the time of calculating the current limit value; and acorrection unit configured to correct the current limit value based onthe estimated polarization state, the battery control device beingconfigured to output the current limit value corrected by the correctionunit as an allowable charge/discharge current value of the battery. 2.The battery control device according to claim 1, wherein the currentlimit value calculation unit calculates a current limit value of abattery based on an open circuit voltage of the battery, upper and lowerlimit voltages set in the battery, and a battery internal resistance inthe case where a constant current flows to the battery from anon-polarization state for a predetermined time, and the correction unitcalculates a polarization voltage in a case where a battery in thepolarization state estimated by the estimation unit is maintained in acurrent zero state for the predetermined time, and the current limitvalue is corrected by using the corrected current value corresponding tothe calculated polarization voltage.
 3. The battery control deviceaccording to claim 2, wherein the battery internal resistance iscalculated based on a DC resistance of a battery, an open circuitvoltage change amount per unit current of the battery, and apolarization resistance of the battery.
 4. The battery control deviceaccording to claim 2, wherein the correction unit calculates thecorrected current value based on the battery internal resistance and thepolarization voltage.
 5. The battery control device according to claim2, wherein the polarization voltage is calculated by a product of acoefficient indicating a temporal change in the polarization voltagewhen a battery current is zero and a polarization voltage in thePolarization state estimated in the estimation unit.
 6. The batterycontrol device according to claim 2, wherein the polarization stateestimated by the estimation unit is initialized at the time ofactivating the battery control device or at the time of activating aload connected to the battery.
 7. The battery control device accordingto claim 5, wherein at least one of the battery internal resistance, thecoefficient indicating the temporal change of the polarization voltagewhen the battery current is zero, and the upper and lower limit voltagesis set to a value corresponding to at least one of a batterytemperature, a battery charging rate, and a current flowing through thebattery.